This invention relates to adhesion aids for increasing the adhesion of polymers to inorganic surfaces and the methods for increasing this adhesion. More specifically, the invention relates to benzocyclobutene-functional silanes and their use as adhesion aids.
Adhesion of polymers in inorganic surfaces is often a critical factor in the reliability of the polymer for the desired application. For example, in the aerospace industry, a polymer matrix frequently bonds two metal surfaces. Inadequate bond strength can lead to catastrophic failure. In the electronics industry, "die attach" adhesives are necessary to bond the inactive side of a semiconductor chip to the electronic package. Bond strength is also important for materials used as insulating layers in multilayered electronic devices. Polymers are replacing inorganic materials for these and other electronic applications because of many desirable properties, such as low dielectric constant, low moisture pickup, and unique fabrication opportunities. Without adequate bond strength, the polymer is a poor candidate for replacing standard inorganic materials.
By far the most prevalent and widely studied adhesion aids for increasing the adhesion of polymers to inorganic surfaces are the organosilanes (see, for example, the comprehensive work on organosilanes in Plueddemann, Silane Coupling Agents, Plenum Press, 233 Spring Street, New York, N.Y. (1982)). Organosilanes improve adhesion by forming a bond between the polymer matrix and the inorganic surface, and by increasing the ability of the resin to "wet" the surface before cure. Although the particular mechanism by which bonding occurs is uncertain, it is believed that the silane group of the organosilane couples with the surface via hydrolysis and the chosen organic functionality of the organosilane reacts with the polymer matrix. Surface wetting of the resin on the inorganic surface is believed to be generally improved by providing a moisture-free surface.
A catalog published by Petrarch Systems, Inc. (Bristol, Pa.), entitled "Silicon Compounds", 1984, discloses at pages 71-74 silane coupling agent chemistry and a guide for selecting coupling agents for different thermosets and thermoplastics. Although a number of different coupling agents are disclosed for varying applications, the development of new polymeric systems for aerospace and electronics applications, such as those described above, prompts the need for new organosilane coupling agents. In particular, an organosilane adhesion aid improving adhesion between an inorganic surface and polymers derived from benzocyclobutene (BCB) is desired. BCB-derived polymers are based on relatively new technology and offer outstanding thermal stability at high temperatures, solvent resistance and low dielectric constants (see, for example, U.S. Pat. No. 4,540,763). An organosilane coupling agent that could effectively improve the adhesion of BCB-derived polymers would greatly enhance the utility of the polymers.